Electrical transmission and distribution equipment within a distribution system operates at voltages within a fairly narrow range under normal conditions. However, system disturbances, such as lightning strikes and switching surges, may produce momentary or extended voltage levels that greatly exceed the levels experienced by the equipment during normal operating conditions. These voltage variations often are referred to as over-voltage conditions.
If not protected from over-voltage conditions, critical and expensive equipment, such as transformers, switching devices, computer equipment, and electrical machinery, may be damaged or destroyed by over-voltage conditions and associated current surges.
Over-voltage protection electrical devices interconnect sources of energy, such as transformers, switching devices, and circuit breakers, to distribution systems through high voltage conductors.